The solid oxide cell is an environmentally friendly and highly efficient energy conversion technology that can convert chemical energy directly to electricity in the fuel cell mode (SOFC) and vice versa in the electrolysis mode (SOEC). This technology has wide stationary and mobile applications and is of interest in power applications (e.g., transportation and power grid applications), in fuel production and energy storage, in chemical synthesis, and as an electrolyzer in various applications (e.g., pressurized oxygen production in medical applications). In general, a solid oxide cell includes a solid oxide ionic (or protonic) conducting material layer as electrolyte separating two electrodes that are also based on ceramics that become electrically or ionically active at relatively high temperatures. In the fuel cell mode oxygen is reduced at a first electrode (the cathode) to form oxygen ions that diffuse across the electrolyte and serve to oxidize the fuel, e.g., hydrogen gas, carbon monoxide gas, to form water and carbon dioxide gases, respectively, at the second electrode (the anode) in order to produce electricity. The process is reversed in the electrolysis mode during which water can be electrolyzed to produce hydrogen and oxygen gases, or carbon dioxide can be electrolyzed to produce carbon monoxide and oxygen gases.
Among various configuration designs, micro-tubular solid oxide cells (MT-SOFCs) have attracted increasing attention due to the advantages of good thermal cycling stability, good thermal shock resistance, easy sealing, high volumetric power density, and quick start-up capability. Unfortunately, the micro-tubular configuration imposes great challenges on fabrication process designs, especially when the diameters of the micro-tubes reach millimeter or sub-millimeter scales, which are required to meet volumetric power density goals. A phase inversion-based spinning method has been successfully demonstrated for the fabrication of anode-supported MT-SOFCs. Typical microtubular anode substrates prepared by this method have the feature of multiple-layered microstructures, with a sponge-like layer sandwiched by two thicker layers and including thin but relatively dense skin layers covering the inner and outer surfaces of the anode. The thick layers define large continuous finger-like pores perpendicular to the sponge-like layer, but both the sponge-like layer and the skin layers contain small and non-continuous pores. As a result, the porosity of these structures is very low. These anode substrates, albeit unique, show serious disadvantages for facile fuel/gas transport as, although the thick finger-like layers do facilitate gas transport, the poor transport properties of the sponge-like layer and the thin skin layer of the inner surface of the substrate can significantly increase resistance to fuel/gas diffusion. This in turn can severely deteriorate electrochemical performance of MT-SOFCs.
A need exists for improved methods for synthesizing microtubular electrodes for use in solid oxide fuel/electrolysis cells. For instance, a method that can provide a microtubular electrode substrate that can demonstrate improved fuel/gas diffusion can provide for improved electrochemical performance of MT-SOFCs.